In the early 1970's, several investigators demonstrated the existence of two .alpha.-Galactosidase isozymes designated A and B, which hydrolyzed the .alpha.-galactosidic linkages in 4-MU-and/or .rho.-NP-.alpha.-D-galactopyranosides (Kint, 1971, Arch. Int. Physiol. Biochem. 79:633-644; Beutler & Kuhl, 1972, Amer. J. Hum. Genet. 24:237-249; Romeo, et al., 1972, FEBS Lett. 27:161-166; Wood & Nadler, 1972, Am. J. Hum. Genet. 24:250-255; Ho, et al., 1972, Am. J. Hum. Genet. 24:256-266; Desnick, et al., 1973, J. Lab. Clin. Med. 81:157-171; and Desnick, et al., 1989, in The Metabolic Basis of Inherited Disease, Scriver, C. R., Beaudet, A. L. Sly, W. S. and Valle, D., eds, pp. 1751-1796, McGraw Hill, New York). In tissues, about 80%-90% of total .alpha.-Galactosidase (.alpha.-Gal) activity was due to a thermolabile, myoinositol-inhibitable .alpha.-Gal A isozyme, while a relatively thermostable, .alpha.-Gal B, accounted for the remainder. The two "isozymes" were separable by electrophoresis, isoelectric focusing, and ion exchange chromatography. After neuraminidase treatment, the electrophoretic migrations and pI value of .alpha.-Gal A and B were similar (Kint, 1971; Arch. Int. Physiol. Biochem. 79:633-644), initially suggesting that the two enzymes were the differentially glycosylated products of the same gene. The finding that the purified glycoprotein enzymes had similar physical properties including subunit molecular weight (.about.46 kDa), homodimeric structures, and amino acid compositions also indicated their structural relatedness (Beutler & Kuhl, 1972, J. Biol. Chem. 247: 7195-7200; Callahan, et al., 1973, Biochem. Med. 7: 424-431; Dean, et al., 1977, Biochem. Biophys. Res. Comm. 77:1411-1417; Schram, et al., 1977, Biochim. Biophys. Acta. 482:138-144; Kusiak, et al., 1978, J. Biol. Chem. 253:184-190; Dean, et al., 1979, J. Biol. Chem. 254:10001-10005; and Bishop, et al., 1980, in Enzyme Therapy in Genetic Disease:2, Desnick, R. J., ed., pp. 17-32, Alan R. Liss, Inc., New York). However, the subsequent demonstration that polyclonal antibodies against .alpha.-Gal A or B did not cross-react with the other enzyme (Beutler & Kuhl, 1972, J. Biol. Chem. 247:7195-7200; and Schram, et al., 1977, Biochim. Biophys. Acta. 482:138-144); that only .alpha.-Gal A activity was deficient in hemizygotes with Fabry disease (Kint, 1971; Arch. Int. Physiol. Biochem. 79: 633-644; Beutler & Kuhl, 1972, Amer. J. Hum. Genet. 24:237-249; Romeo, et al., 1972, FEBS Lett. 27:161-166; Wood & Nadler, 1972, Am. J. Hum. Genet. 24:250-255; Ho, et al., 1972, Am. J. Hum. Genet. 24:256-266; Desnick, et al., 1973, J. Lab. Clin. Med. 81:157-171; Desnick, et al., 1989, in The Metabolic Basis of Inherited Disease, Scriver, C. R., Beaudet, A. L. Sly, W. S. and Valle, D., eds, pp. 1751-1796, McGraw Hill, New York; and, Beutler & Kuhl, 1972, J. Biol. Chem. 247:7195-7200); and that the genes for .alpha.-Gal A and B mapped to different chromosomes (Desnick, et al., 1989, in The Metabolic Basis of Inherited Disease, Scriver, C. R., Beaudet, A. L. Sly, W. S. and Valle, D., eds, pp. 1751-1796, McGraw Hill, New York; deGroot, et al., 1978, Hum. Genet. 44:305-312), clearly demonstrated that these enzymes were genetically distinct.